1. Field of the Invention
This invention relates to a process for the preparation of .epsilon.-(.gamma.-glutamyl)-lysine from lysine glutamate.
2. Description of the Prior Art
.epsilon.-(.gamma.-GLUTAMYL)-LYSINE (EPSILON-(GAMMA-GLUTAMUYL)-LYSINE) IS ONE OF THE POSSIBLE CONDENSATION PRODUCTS OF LYSINE, AN ESSENTIAL BASIC AMINO ACID, AND GLUTAMIC ACID, AN ACID AMINO ACID. It is not a peptide in the accepted sense of the term, because the lysine is engaged by its amino group in the .epsilon.-position and the glutamic acid by its carboxlic group in the .gamma.-position, whereas genuine peptides and proteins consist in principle of amino acids condensed on their amino or carboxylic groups in the .alpha.-position.
However, this .epsilon.-derivative of lysine is of particular interest as a dietetic additive because it can be used instead of L-lysine or instead of peptides or proteins rich in lysine for enriching foods poor in lysine, such as cereals, as indicated in German Patent Application No. 2,423,089.
The advantage of a practical, inexpensive synthesis will be immediately appreciated. Unfortunately, both on account of the multiplicity of amino and carboxylic acid reaction sites and on account of the tendecy which glutamic acid has to cyclise into pyrrolidone carboxylic acid or pyroglutamic acid, synthesis by direct coupling of the two elemental amino acids is only possible by adopting the conventional methods for the chemical synthesis of peptides, which comprises protecting certain reaction sites whilst activating others, and removing the protective and activating groups on completion of the reaction from the entities present. This leads to a reaction with a multiplicity of stages and only modest yields. In addition, these groups are removed in the present case by hydrogenolysis on palladium so as to avoid rearrangements (cf. for example J. Biol. Chem. 248 (8), 2536, 1973), which results in high production costs.